Digital reflection coefficient detector

ABSTRACT

There are shown herein an apparatus and method for indicating and storing the modulus of the reflection coefficient in a radio frequency system. The apparatus makes use of voltages Er and Ef. Voltage Er is a measure of the power reflected back from the load. Voltage Ef is a measure of the forward power sent toward the load by the source. The analog quantities Er and NEf are applied to a comparator, the output of which is utilized to control an up-down counter which stores the quantity N, the modulus of the reflection coefficient. The up-down counter controls a digital to analog converter which utilizes the quantity Ef as a reference and produces the analog output NEf.

United States Patent Oomen 51 Nov. 28, 1972 [s41 DIGITAL REFLECTION COEFFICIENT OTHER PUBLICATIONS DETECTOR Burkart et al., Digital Motion Verifier, IBM Technical [72] Inventor: Johannes A. F. Oomen, Cincinnati, Disclosure Bulletin, Feb. 1971, p 2580.

Ohio

Primary Examiner-Starfley T. Krawczewicz [73] Assignee. Avoo Corporation, CIncInnau, OhlO Attorney a les M Hogan [22] Filed: May 24, 1971 21 Appl. No.: 146,069 [57] ABSTRACT There are shown herein an apparatus and method for 52 US. Cl ..324/57R, 324/58 B indicating and swing the wdulus reflect 51 Im. Cl. ..G01r 27/00 efficient in a radi frequency system The apparatus 58 Field of Search ..324/57 R,-58 B, 58.5 B; makes vdtages Er and Rage Er is a 307/222 328/44 sure of the power reflected back fi'orn the load. Voltage E, is a measure of the forward power sent toward [56] References Cited the load by the source. The analog quantities E, and NE, are applied to a comparator, the output of which UNITED STATES PATENTS is utilized to control an up-down counter which stores t the quantity N, the modulus of the reflection coeffiziz 3: cient. The up-down counter controls a dig tal to analog converter which utilizes the quantity E, as a FOREIGN PATENTS OR APPLICATIONS reference and produces the analog Output 494,130 6/1953 Canada ..324/57 2 Claim, 2 Drawing Figures DIRECTIONAL COUPLER I6 |4 I3 I 5 AMPLIFIER DETECTOR '2 H DETECTOR AMPLIFIER I9 I 20 OMPAR ATOR N Ef Olga-[6E0 Ef '7 C CONVERTER 11 36- 38. BINARY 37--- DECISION f 23 GATE GATE 24 UP DOWN 2l I COUNTER F PULSES 25 PATENTEDIIIIIea I972 3.704.409

DIRECTIONAL L COUPLER l6 l4 ,5 /I 5 AMPLIFIER DETECTOR DETECTOR AMPLIFIER DIGITAL TO Er f ANALOG f BINARY 38 DECISION -39 274 has 26 ,GATE GATE w UP DOWN 23 I I I 24 COUNTER 25 PULSES i JOHANNES A. E OOM EN INYVEN'IOR. I

. ATTORNEY.

DIGITAL REFLECTION COEFFICIENT DETECTOR BACKGROUND OF THE INVENTION The degree to which a transmission line or other radio frequency system of lumped and/or distributed parameters is tuned has generally been established by measuring reflected power. However, reflected power depends upon a number of variables including the reflection coefficient of the load and also the output impedance and power of the source. It would be desirable to provide a device and process for measuring the reflection coefficient modulus directly and indicating and storing it digitally, independent of the source impedance and power output variables.

The primary object of the present invention is to provide such device and process.

My invention is based in part on a recognition of the fact that the definition of reflection coefficient is independent of source impedance or source output power. That is to say E, reflected voltage E,= forward voltage V The inventive combination utilizes measures of for ward and reflected voltage. It is known to the art that a bidirectional coupler permits simultaneous sampling of signal flow in two directions. It is therefore used to furnish the required forward voltage and reflected voltage parameters. See Airborne Radar, Grayson Merrill ed., p. 548 (New York: D. Van Nostrand Co., Inc., 1961). For this reason a bidirectional coupler will be shown in block diagram herein, without a detailed description.

In accordance-with the invention an analog to digital converter is utilized to perform a dividing function and to indicate the result. The preferred form of converter herein disclosed, by way of illustration and not of limitation, is the feedback voltage-input encoder type. For background and state-of-the-art literature on feedback voltage-input encoders and ladder systems for converting a digital number in an up-down register to an analog voltage, please see the following: Digital Computer Components and Circuits, R. K. Richards, pp. 459-503, particularly pages 489-491, (New York: D. Van Nostrand Co., Inc., 1957); Handbook of Telemetry and Remote Control, Elliot L. Gruenberg, pp. 11-13 to 11-20, particularly p. 11-19, (New York: McGraw Hill Book Co., Inc. 1967); Digital Computer and Control Engineering, Robert Steven Ledley, pp. 739-763, (New York: McGraw Hill Book Co., Inc. 1960); Aerospace Telemetry, Harry L. Stiltz, ed., pp. 179-183, (Englewood Cliffs, N.J.: Prentice Hall, Inc., 1961); Campurer Handbook, Harry D. Huskey and Granino A. Korn, ed., pp. 18-29 to 18-46, (NewYork: McGraw Hill Book Co., Inc., 1962); and Digital and Sampled Data Control Systems, Julius E. Tou, pp. 377-404, (New York: McGraw Hill Book Co., Inc., 1959).

THE DRAWINGS For a better understanding of the invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following description of the accompanying drawings, in which:

FIG. 1 is a block diagram form of a preferred reflection coefficient detector in accordance with the invention, and

FIG. 2 is a circuit diagram of a converter circuit of the ladder type, suitable for use in the system.

DETAILED DESCRIPTION OF THE INVENTION Referring first to FIG. 1, there is shown a bidirectional coupler 10 which is so arranged as to provide a forward power output 11 and a reflected power output 12, respectively coupled to detectors 13 and 14. The directional coupler 10 is disposed between an r.f. (i.e. radio frequency) source and r.f. load of a radio frequency system to be tuned and it'incorporates the customary output ports 11 and 12. The detectors 13 and 14 have outputs respectively coupled to output lines 17 and 18, respectively, via amplifiers 15 and 16, respectively.

The elements 10-18 function collectively to provide reflected voltage, the parameter 13,, on line 18 and forward voltage, the parameter E, on line 17.

In accordance with the invention two analog inputs are applied to a comparator device 19. One is the reflected voltage E, and the other is a product of N and E,, N being the modulus of the reflection coefficient and E, being the forward voltage.

The dividing function by reason of which the modulus of the reflection coefficient N is directly registered by an updown counter 21 is performed by the elements now described.

A source of clock pulses indicated at 22 is coupled via additive gate 23 and subtractive gate 24 to up input 25 and down input 26, respectively, of the up-down counter 21. These gates are individually coupled to the up output 27 and the down output 28 of a binary decision network 29. The binary decision network 29 has an input coupled to the output of the comparator 19, as shown at 30. The operation is such that when E, decreases with respect to an established equilibrium position, the quantity NE, also decreases and the output of the comparator on line 30 is such that the binary decision network 29 activates its up output 27, activating gate 23 so that additional pulses flow from the source 22 into the counter 21, to reflect the increase in N, until a new equilibrium is reached. By contrast, an

increase in the forward voltage is accompanied by a signal on the output 30 of comparator 19 of such character that the binary decision device 29 activates its control output 28, activating gate 241, so that pulses are gated from source 22 via line 26 to subtract from the digital number registered in the up-down counter 21. Accordingly the up-down counter functions continuously to store, to record, and to indicate the modulus of the reflection coefiicient, i.e., N.

It will be observed that, in accordance with the concepts of the invention, the analog quantities E, and E, are first derived. One of them, to-wit: the reflected voltage, is then directly utilized as an analog input to the comparator of a conventional feedback voltage-input encoder. The other quantity E used as the reference voltage for a digital to analog converter, which supplies the other comparator input NE, on its output line 31. In effect, two analog signals are divided and a binary result is registered in the up-down counter 21.

fashion either to the reference voltage E, or to ground potential. It will be understood that the switching is controlled electronically by the up-down counter 21. The ladder network of FIG. 2 produces an output voltage which is an analog function of the digital number indicated by the settings of the four switches. As indicated, switching is electrically performed by the outputs 36, 37, 38 and 39 of the up-down counter 21.

It has been shown that the digital number in the up down counter represents the ratio between the quantities E,- and E,. Strictly speaking, the number registered in the up-down counter is the modulus of the reflection coefficient.

While there has been shown and described what is at present believed to be the preferred embodiment of the invention, it will be understood by those skilled in the art that various modifications and changes may be made therein without departing from the proper scope of the invention as defined by the claimshereto ana comparator having a first input for the voltage E and also a second input, an up down counter, a digital to analog converter having an output coupled to the comparator and having also an input, the quantity E; being applied to said converter input and the quantity NE being the converter output so that the comparator output produces a signal indicating whether E,- or NE, is greater, a source of clock pulses, 1 and means coupled to the comparator for channeling the pulses to the up-down counter in such fashion as to increase the count when the quantity E prevails and to decrease the count when the quantity NE, prevails, whereby the up-down counter registers the modulus N of the reflection coefficient.

2. In a radio frequency system in which power is transferred from a source to a load, a reflection coefficient modulus detector comprising:

means for deriving the reflected voltage or quantity 7'! means for deriving the forward voltage or quantity l, converter means providing digital storage and having an input to which the voltage E, is applied as a reference and also an analog output producing a voltage equal the product of E;and N, means for comparing the quantities E; and NE, and

producin abidirectional control signal and means coup ed to the converter means for utilizing the bidirectional control signal to establish the digital settings of said converter, whereby said settings are a measure of N, the reflection coefficient modulus.

t i i 

1. In a radio frequency system in which power is transferred from a source to a load, the combination of: means for deriving the reflected voltage or quantity Er, means for deriving the forward voltage or quantity Ef, and a feedback voltage input encoder comprising: a comparator having a first input for the voltage Er and also a second input, an up-down counter, a digital to analog converter having an output coupled to the comparator and having also an input, the quantity Ef being applied to said converter input and the quantity NEf being the converter output so that the comparator output produces a signal indicating whether Er or NEf is greater, a source of clock pulses, and means coupled to the comparator for channeling the pulses to the up-down counter in such fashion as to increase the count when the quantity Er prevails and to decrease the count when the quantity NEf prevails, whereby the up-down counter registers the modulus N of the reflection coefficient.
 2. In a radio frequency system in which power is transferred from a source to a load, a reflection coefficient modulus detector comprising: means for deriving the reflected voltage or quantity Er, means for deriving the forward voltage or quantity Ef, converter means providing digital storage and having an input to which the voltage Ef is applied as a reference and also an analog output producing a voltage equal the product of Ef and N, means for comparing the quantities Ef and NEr and producing a bidirectional control signal, and means coupled to the converter means for utilizing the bidirectional control signal to establish the digital settings of said converter, whereby said settings are a measure of N, the reflection coefficient modulus. 